We will investigate host gene effects upon the development of Rous sarcoma virus (RSV) induced tumors in crosses of inbred lines and in noninbreds. The primary focus of the work will be the B locus (MHC) which has a major role in the fate of RSV-induced tumors in this species. First, we will investigate recombinants within the MHC and study their possible association with sarcoma regression. Second, the importance of the lymphocyte in tumor rejection using acridine orange staining and electrophoretic procedures will be studied. Third, we will explore the possible association of host genotype with metastatic tumor.